Biochemical reactions remote-sensitized by excitons propagating across macroscopic distances along biological fibers: Isomerization of 11-cis-retinal

Presently we report a second example of a biochemical reaction sensitized remotely by excitons (electronic excited states) efficiently transferred along intermediate filaments (IFs) over macroscopic distances. IFs are excellent conductors of energy in the form of excitons, with the efficiency of ca. 0.53 reported in vitro. Excitons were generated by visible light and propagated along Müller cell (MC) intermediate filaments, about 100 μm long. These experiments used a capillary matrix filled by MC IFs extracted from porcine retina. Excitons induced efficient isomerization of 11-cis- to all-trans-retinal, with the reaction quantum yield φ_cis/trans = 0.347 obtained for 11-cis-retinal concentration of 1.0 × 10⁻³ M (0.284 g/L) using 546 nm light at 6.87 mW/cm² power density. Exciton quantum yield φ_exc at 546 nm was also measured in function of radiation power density, with nonlinearity indicative of biphotonic processes. This is the first case of biphotonic processes occurring at such low light intensities with steady-state illumination. The present results support quantum mechanism of high-contrast vision of vertebrate eyes.